The space shuttle's mid-deck was a multipurpose area. Astronauts slept here, food was stored and prepared, scientific research was carried out, and the toilet utilized. It provided crew module access on the ground through the main hatch and in space through the airlock to the payload bay and International Space Station (ISS). During launch and landing, three to four astronauts sat in the mid-deck, blind to the outside except for one tiny window in the main hatch.